The present invention relates to techniques effective in semiconductor devices with a clock oscillation circuit generating a clock signal used for circuit operation.
Semiconductor devices, such as general-purpose microcomputers, need to reduce the number of external components for miniaturization and cost reduction of equipment. Some semiconductor devices have an on-chip oscillator, which uses no external components, such as a crystal oscillator, in a clock oscillation circuit which generates a clock signal supplied to internal modules, such as a CPU (Central Processing Unit) and a peripheral functional block.
Frequency accuracy is an important characteristic of the on-chip oscillator. This is a frequency variation relative to a power supply variation or a temperature variation. The low frequency accuracy of the on-chip oscillator limits the application of the on-chip oscillator as the alternative component of an external oscillator.
Widening the application range needs to increase the frequency accuracy of the on-chip oscillator. The range can be further widened by heightening the frequency accuracy and covering a wide oscillation frequency range. General-purpose microcomputers usually allows users to change the settings according to an intended application.
For example, the on-chip oscillator, requiring high frequency accuracy, is performed temperature trimming in order to improve the frequency accuracy. Temperature trimming sets a control signal to cancel the temperature dependence of a circuit and that of a device that is being used.
Trimming at two temperature points can cancel the first-order temperature coefficient. Trimming at three temperature points can cancel the second-order temperature coefficient, too.
An example of this type of clock oscillation circuits is the one which stabilizes the oscillation frequency and heightens the oscillation accuracy by connecting a current-controlled oscillator, a frequency divider, a period comparison circuit, an integration circuit, and a voltage-current conversion circuit in series, returning the output current of the voltage-current conversion circuit at the final stage to the input side of the current-controlled oscillator at the first stage, and using the output of the current-controlled oscillator as the oscillation output (see Japanese Patent Laid-Open No. 2002-300027 (Patent Document 1)).
Moreover, a voltage generation circuits generating a plurality of voltages with high accuracy is the one including a reference voltage generation circuit, a differential amplifier, a P-channel MOS (Metal Oxide Semiconductor) transistor, a switching transistor, an output node, and a first to a third resistor strings. The third resistor string is between other input terminal of the differential amplifier and a ground. Even when the resistance of the first resistor string between the drain of the P-channel MOS transistor and an output node and that of the second resistor string between the output node and the other input terminal of the differential amplifier, which differs from that of the first resistor string, are selected and controlled, these resistances are selected and controlled so that a sum of the resistance of the first resistor string and that of the second resistor string is constant (see Japanese Patent Laid-Open No. 2007-293545 (Patent Document 2)).